Tuning optical and electrical transport properties of Bi2Se3 with Ca*

We have systematically tuned the carrier type and density in Bi$_{2}$Se$_{3}$ single crystals by introducing a calcium dopant. By controlling Ca-concentration x in Ca$_{x}$Bi$_{2-x}$Se$_{3}$, a minimum carrier density of $\sim $ $1 \times 10^{17}$ cm$^{-3}$ is achieved in both n- and p-type materials. The Fourier transform infrared (FTIR) measurements were carried out in samples with different doping levels to obtain the inter-band transition energy, sample thickness, and the plasma frequency. The band gap and reduced effective mass of carriers were determined from the relation between the inter-band transition energy and carrier density. The undoped samples show a high electron density ($\sim $ $5 \times 10^{18}$ cm$^{-3})$ and the electrical resistivity shows a typical metallic behavior. At high magnetic fields (up to 14 T), the undoped samples show the Shubnikov-de Haas oscillations. Near the compensation point or x=1.2{\%}, the electrical resistivity shows an insulating behavior with a low temperature saturation. This work was supported in part by DOE and NSF.